Subject: Siphon Simulation in SWMM 5 and InfoSWMM
A Siphon is simulated in SWMM 5 and InfoSWMM using the basic node and link data and downstream boundary condition:
1. Inflow can be time series, dry weather flow pattern, wet weather inflow or Subcatchment Runoff,
2. The boundary condition can be either a free outfall, fixed or time series,
3. The node invert, node maximum depth and node surcharge depth are defined by the user or network,
4. The link lengths, diameters, link offset depths upstream and downstream are defined by the user of the network,
5. The node depths, link flows, link depths and link cross sectional areas are calculated at each time based on the node continuity equation and the link momentum and continuity equation. The link flows are a function of the friction loss, head difference across the link and the difference in the cross sectional areas of the link.
6. In the particular model the Inflow at node MH1 fills up the MH1 depth which causes the links downstream to start flowing – the head difference across the links drives the flow up and over the siphon.